until 1500 BC, all money was cattle, lambs, goats or pigs – live money
that was real life-support wealth, wealth you could actually eat.
Steers were by far the biggest food animal and so they were the highest
denomination of money. The Phoenicians carried their cattle with
them for trading but these big creatures proved to very cumbersome on long
voyages. This was the time when Crete was the headquarters of the
big-boat people and their new supreme weapon – the lines-of-supply-control
ship. Crete was called the Minoan civilization, the bull civilization,
worshippers of the male fertility god.
The pair of joined bulls horns symbolized that the particular ship carried real-wealth traders – that there were cattle on board to be exchanged for local-wealth items…
Graduating from carrying cattle along for trading in 1500 BC, the Phoenicians invented metal money, which they first formed into iron half-rings that looked like a pair of bull’s horns. (Many today mistake them for bracelets.) Soon the traders found that those in previously unvisited foreign countries had no memory of the cattle-on-board trading days and didn’t recognize the miniature iron bull horn. If metal was being used for trading then there were other kinds of metal they preferred trading with people – silver, copper and gold were easy to judge by hefting and were more aesthetically pleasing than the forged iron bull horn symbols.
This soon brought metal coinage into the game of world trading with the first coin bearing the image of the sovereign of the homeland of the Phoenicians."
--- from Critical Path by R. Buckminster Fuller